Everybody is different which is why we supply options. If you care to take a second look you will realise that you can enter any border or font size you wish.
The dropdown is there to give you an easy to access set of selections.
I just downloaded the latest version of Verification Engine (2.2.0.5) and apparently you are not able to make the border smaller than 8 pixels. 8 is the smallest number in the list and if you type in a smaller number it reverts back to 8 when you press “OK”.